1. Field of the Invention
The present invention relates to an automatic focusing apparatus in a camera.
2. Description of the Related Art
In recent digital still cameras (digital cameras), object images are recorded as electric digital image data. In the digital cameras, a CCD image pickup device (CCD image sensor) is employed in place of a silver-halide film.
Conventional compact digital still cameras are provided with a unifocal or bifocal photographing lens. In general, the light receiving surface area of the CCD image pickup device is smaller than that of the camera using the silver-halide film. Consequently, the focal length of the photographing lens of a digital camera is shorter than that of the camera using the silver-halide camera for the same angle of view, and hence the depth-of-field (focal depth) of the digital still camera is greater than that of the camera using the silver-halide camera. Therefore, a pan-focus can be obtained by the wide-angle unifocal lens.
To make it possible for a digital camera to carry out macro-photographing, an object in a distance range from a few centimeters (near point) from the digital camera to the infinite distance (far point) must be accommodated in the depth-of-field. To this end, the f-number of the photographing lens must be considerably increased and the focal length thereof must be considerably decreased. This is impractical. If the photographing lens is made of a zoom lens, the depth-of-field (focal depth) at the long focal length is small, and hence an automatic focusing apparatus is needed.
However, in conventional automatic focusing apparatuses, there are times when, depending on the conditions of the object, it is impossible to focus correctly, as is well known. There has been a need for an automatic focusing apparatus in which the automatic focus control can be executed for almost all object distance conditions, or where no or little images that are out-of-focus are formed.
It is an object of the present invention to provide an automatic focusing apparatus of a camera in which the distance range of an object on which the photographing lens can be focused even under the conditions that no automatic focusing operation is available can be expanded or the probability of a formation of an object image that is out-of-focus can be reduced.